Here is the full list of all 20 Nix: Ashes of the Phoenix achievements.
Use any spell!
Play in sandbox mode
Collect 5000G
Kill 20000 bats
Death 50 times
Kill 1000 enemies using the phoenix pet
Reach Lvl 2 for the 1st time
Defeated by the first boss
Kill the first boss using the phoenix pet
Reach Lvl 10 for the 1st time
Kill 1000 enemies with range attack
Kill 5000 skeletons
Kill 5000 wolves
Enter Raid for the 1st time
Using Modifier card for the 1st time
Kill 100 enemies using fire spells
Survive the Horde
Kill 5000 bats
Kill 10000 bats
Kill 1st Level Boss